Hybrid stent

ABSTRACT

A stent includes a high radial/crush force segment and a highly flexible segment. In an aspect, a plurality of first ring struts connected such that each of the plurality of first rings comprises a sinusoidal pattern having a plurality of apices and troughs, each first ring connected to an adjacent first ring by at least one connector. The connector extends from a ring strut of the first ring from a position near an apex of the first ring to a ring strut of the adjacent first rings near an apex of the adjacent ring, and a second stent segment comprises a plurality of second rings connected to one another to form a series of second rings.

BACKGROUND Field of the Invention

Disclosed herein are stents for implantation within the body and methodsfor delivery and/or deployment. Certain embodiments disclosed herein maybe used in procedures to treat May-Thurner syndrome and/or deep venousthrombosis and the resulting post-thrombotic syndrome.

Description of the Related Art

May-Thurner syndrome, also known as iliac vein compression syndrome, isa condition in which compression of the common venous outflow tract ofthe left lower extremity may cause various adverse effects, including,but not limited to, discomfort, swelling, pain, and/or deep venousthrombosis (DVT) (commonly known as blood clots). May-Thurner syndromeoccurs when the left common iliac vein is compressed by the overlyingright common iliac artery, leading to stasis of blood, which may causethe formation of blood clots in some individuals. Other, less common,variations of May-Thurner syndrome have been described, such ascompression of the right common iliac vein by the right common iliacartery.

While May-Thurner syndrome is thought to represent between two to fivepercent of lower-extremity venous disorders, it frequently goesunrecognized. Nevertheless, it is generally accepted that May-Thurnersyndrome is about three times more common in women than it is in men andtypically manifests itself between the age of twenty and forty. Patientsexhibiting both hypercoagulability and left lower extremity thrombosismay be suffering from May-Thurner syndrome. To confirm that diagnosis,it may be necessary to rule out other causes for hypercoagulable state,for example by evaluating levels of antithrombin, protein C, protein S,factor V Leiden, and prothrombin G20210A.

By contrast to the right common iliac vein, which ascends almostvertically parallel to the inferior vena cava, the left common iliacvein takes a more transverse course. Along this course, it lies underthe right common iliac artery, which may compress it against the lumbarspine. Iliac vein compression is a frequent anatomic variant—it isthought that as much as 50% luminal compression of the left iliac veinoccurs in a quarter of healthy individuals. However, compression of theleft common iliac vein becomes clinically significant only if suchcompression causes appreciable hemodynamic changes in venous flow orvenous pressure, or if it leads to acute or chronic deep venousthrombosis, which will be discussed in more detail below. In addition tothe other problems associated with compression, the vein may alsodevelop intraluminal fibrous spurs from the effects of the chronicpulsatile compressive force from the overlying artery.

The narrowed, turbulent channel associated with May-Thurner syndrome maypredispose the afflicted patient to thrombosis. And, the compromisedblood flow often causes collateral blood vessels to form—most oftenhorizontal transpelvis collaterals, connecting both internal iliac veinsto create additional outflow possibilities through the right commoniliac vein. Sometimes vertical collaterals are formed, most oftenparalumbar, which can cause neurological symptoms, like tingling andnumbness.

Current best practices for the treatment and/or management ofMay-Thurner syndrome is proportional to the severity of the clinicalpresentation. Leg swelling and pain is best evaluated by vascularspecialists, such as vascular surgeons, interventional cardiologists,and interventional radiologists, who both diagnose and treat arterialand venous diseases to ensure that the cause of the extremity pain isevaluated. Diagnosis of May-Thurner syndrome is generally confirmed oneor more imaging modalities that may include magnetic resonancevenography, and venogram, which, because the collapsed/flattened leftcommon iliac may not be visible or noticed using conventionalvenography, are usually confirmed with intravascular ultrasound. Toprevent prolonged swelling or pain as downstream consequences of theleft common iliac hemostasis, blood flow out of the leg should beimproved/increased. Early-stage or uncomplicated cases may be managedsimply with compression stockings. Late-stage or severe May-Thurnersyndrome may require thrombolysis if there is a recent onset ofthrombosis, followed by angioplasty and stenting of the iliac vein afterconfirming the diagnosis with a venogram or an intravascular ultrasound.A stent may be used to support the area from further compressionfollowing angioplasty. However, currently available stenting optionssuffer from several complications—including severe foreshortenting, lackof flexibility (which can force the vessel to straighten excessively),vessel wear and eventual performation, increased load on and deformationof the stent causing early fatigue failure, and/or impedence of flow inthe overlying left iliac artery potentially causing peripheral arterialdisease. The compressed, narrowed outflow channel present in May-Thurnersyndrome may cause stasis of the blood, which an important contributingfactor to deep vein thrombosis.

Some patients suffering from May-Thurner syndrome may exhibit thrombosiswhile others may not. Nevertheless, those patients that do notexperience thrombotic symptoms may still experience thrombosis at anytime. If a patient has extensive thrombosis, pharmacologic and/ormechanical (i.e., pharmacomechanical) thrombectomy may be necessary. Thehemostasis caused by May-Thurner syndrome has been positively linked toan increased incidence of deep vein thrombosis (“DVT”).

Deep vein thrombosis, or deep venous thrombosis, is the formation of ablood clot (thrombus) within a deep vein, predominantly in the legs. Theright and left common iliac are common locations for deep veinthrombosis, but other locations of occurrence are common. Non-specificsymptoms associated with the condition may include pain, swelling,redness, warmness, and engorged superficial veins. Pulmonary embolism, apotentially life-threatening complication of deep vein thrombosis, iscaused by the detachment of a partial or complete thrombus that travelsto the lungs. Post-thrombotic syndrome, another long-term complicationassociated with deep venous thrombosis, is a medical condition caused bya reduction in the return of venous blood to the heart and can includethe symptoms of chronic leg pain, swelling, redness, and ulcers orsores.

Deep vein thrombosis formation typically begins inside the valves of thecalf veins, where the blood is relatively oxygen deprived, whichactivates certain biochemical pathways. Several medical conditionsincrease the risk for deep vein thrombosis, including cancer, trauma,and antiphospholipid syndrome. Other risk factors include older age,surgery, immobilization (e.g., as experienced with bed rest, orthopediccasts, and sitting on long flights), combined oral contraceptives,pregnancy, the postnatal period, and genetic factors. Those geneticfactors include deficiencies with antithrombin, protein C, and proteinS, the mutation of Factor V Leiden, and the property of having a non-Oblood type. The rate of new cases of deep vein thrombosis increasesdramatically from childhood to old age; in adulthood, about 1 in 1000adults develops the condition annually.

Common symptoms of deep vein thrombosis include pain or tenderness,swelling, warmth, redness or discoloration, and distention of surfaceveins, although about half of those with the condition have no symptoms.Signs and symptoms alone are not sufficiently sensitive or specific tomake a diagnosis, but when considered in conjunction with known riskfactors can help determine the likelihood of deep vein thrombosis. Deepvein thrombosis is frequently ruled out as a diagnosis after patientevaluation: the suspected symptoms are more often due to other,unrelated causes, such as cellulitis, Baker's cyst, musculoskeletalinjury, or lymphedema. Other differential diagnoses include hematoma,tumors, venous or arterial aneurysms, and connective tissue disorders.

Anticoagulation, which prevents further coagulation but does not actdirectly on existing clots, is the standard treatment for deep veinthrombosis. Other, potentially adjunct, therapies/treatments may includecompression stockings, selective movement and/or stretching, inferiorvena cava filters, thrombolysis, and thrombectomy.

In any case, treatment of various venous maladies, including thosedescribed above, can be improved with stents. Improvements in stents forvenous use are therefore desired.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an intravascular stentthat obviates one or more of the problems due to limitations anddisadvantages of the related art.

In an aspect of the present invention, a stent comprises a first stentsegment comprising a plurality of first rings connected to one anotherto form a series of said first rings.

In this aspect, the first rings comprise a plurality of first ringstruts connected such that each of the plurality of first ringscomprises a sinusoidal pattern having a plurality of apices and troughs,each first ring connected to an adjacent first ring by at least oneconnector, the connector extending from a ring strut of the first ringfrom a position near an apex of said first ring to a ring strut of theadjacent first rings near an apex of the adjacent ring.

In this aspect, the stent also includes a second stent segmentcomprising a plurality of second rings connected to one another to forma series of said second rings. In this aspect, the second stent segmentis coupled to the first stent segment; said first stent segment has afirst stiffness and a first crush resistance and the second stentsegment has a second stiffness and a second crush resistance, whereinthe first stiffness is different from the second stiffness and the firstcrush resistance is different from the second crush resistance.

Further embodiments, features, and advantages of the intravascularstent, as well as the structure and operation of the various embodimentsof the intravascular stent, are described in detail below with referenceto the accompanying drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are incorporated herein and form part ofthe specification, illustrate an intravascular stent. Together with thedescription, the figures further serve to explain the principles of theintravascular stent described herein and thereby enable a person skilledin the pertinent art to make and use the intravascular stent.

FIG. 1 shows an inferior-posterior view of the L5 lumbar and thebifurcations of the abdominal aorta and inferior vena cava;

FIG. 2 shows a schematic of the standard overlap of the right commoniliac artery over the left common iliac vein;

FIG. 3 shows a cross-sectional schematic of the arterio-venous systemshown in FIG. 2;

FIG. 4 illustrates radial force as radial resistive force or chronicoutward force;

FIG. 5 illustrates crush resistance force and load on an exemplarystent;

FIG. 6 illustrates an exemplary hybrid stent according to principles ofthe present disclosure;

FIG. 7 illustrates an exemplary reinforcement ring according toprinciples of the present disclosure;

FIG. 8 illustrates an exemplary embodiment of a hybrid stent accordingto principles of the present disclosure;

FIG. 9A, FIG. 9B and FIG. 9C illustrate details of the embodiment ofFIG. 8.

FIG. 10 illustrates an exemplary placement of a hybrid stent accordingto principles of the present disclosure in the left common iliac vein;

FIG. 11 illustrates an exemplary placement of a hybrid stent having aflared end according to principles of the present disclosure in the leftcommon iliac vein;

FIG. 12 illustrates an exemplary extension stent according principles ofthe present disclosure;

FIG. 13 illustrates an embodiment of an extension stent according toprinciples of the present disclosure; and

FIG. 14 illustrates an exemplary placement of a hybrid stent and anextension stent according to principles of the present disclosure in theleft common iliac vein.

FIGS. 15A and 15B illustrate a planar/flattened view of an exemplaryembodiment of a high radial/crush force segment of a stent in acompressed state according to principles of the present disclosure.

FIG. 16 illustrates an exemplary embodiment of a high radial/crush forcesegment of a stent in an expanded state according to principles of thepresent disclosure.

FIGS. 17A, 17B and 17C illustrate a planar/flattened view of anexemplary embodiment of a highly flexible segment of a stent in acompressed state according to principles of the present disclosure.

FIG. 18 illustrates an exemplary embodiment of a highly flexible segmentof a stent in an expanded state according to principles of the presentdisclosure.

FIG. 19 illustrates a transition area between two segments of a hybridstent according to principles described herein.

FIG. 20 illustrates an exemplary connection between a high radial forcesegment and a transition section according to principles describedherein.

FIG. 21 illustrates an embodiment of connectors extending betweenconnectors at points spaced from the apices of the connector.

DETAILED DESCRIPTION

Accurate placement is ideal in all medical interventions, but it isvital in areas where the end that is first deployed is critical. Suchareas include at vessel bifurcations and branch vessels, so that theimplant does not enter or interfere with the portion of the vessel thatdoes not require treatment. Such a bifurcation is present at theinferior vena cava where it branches into right and left iliac veins, asdescribed in more detail below.

May-Thurner syndrome, or iliac vein compression syndrome, occurs in theperipheral venous system when the iliac artery compresses the iliac veinagainst the spine as shown in FIG. 1. FIG. 1 illustrates a vertebra, theright and left common iliac arteries near the bifurcation of theabdominal aorta, and the right and left common iliac arteries near thebifurcation of the inferior vena cava. The bifurcations generally occurnear the L5 lumbar vertebra. Thus, it can be seen that FIG. 1 shows aninferior-posterior view of the L5 lumbar and the bifurcations of theabdominal aorta and inferior vena cava.

As shown, the strong right common iliac artery has compressed the iliacvein causing it to become narrowed. This is one possible, if not aclassic, manifestation of May-Thurner syndrome. Over time, suchnarrowing may cause vascular scarring which can result in intraluminalchanges that could precipitate iliofemoral venous outflow obstructionand/or deep vein thrombosis. As discussed above, venous insufficiency(i.e., a condition in which the flow of blood through the veins isimpaired) can ultimately lead to various deleterious pathologiesincluding, but not limited to, pain, swelling, edema, skin changes, andulcerations. Venous insufficiency is typically brought on by venoushypertension that develops as a result of persistent venous obstructionand incompetent (or subcompetent) venous valves. Current treatments forvenous outflow obstruction include anticoagulation, thrombolysis,balloon angioplasty and stenting.

FIG. 2 illustrates the standard overlap of the right common iliac arteryover the left common iliac vein. The arteries shown include theabdominal aorta 1500 branching into the left common iliac artery 1501and the right common iliac artery 1502. The veins shown include theinferior vena cava 1503 branching into the left common iliac vein 1504and right common iliac vein 1505. It will be understood that the roughdiagram illustrated in FIG. 2 represents the view looking down on apatient laying face-up (i.e., an anterior-poster view of the patient atthe location of the bifurcation of the abdominal aorta 1500 and theinferior vena cava 1503). The overlap of the right common iliac artery1502, which is relatively strong and muscular, over the left commoniliac vein 1504 can cause May-Thurner syndrome by pressing down on thevein 1504, crushing it against the spine, restricting flow, and,eventually, causing thrombosis and potentially partially or completelyclotting off of the left common iliac vein 1504 and everything upstreamof it (i.e., the venous system in the left leg, among others).

FIG. 3 illustrates a cross-section of the arterio-venous system shown inFIG. 2 taken along the gray dotted line. Shown in schematic are theright common iliac artery 1600, the left common iliac vein 1601, and avertebra 1602 of the spine (possibly the L5 lumbar vertebra of thelumbar spine). As can be seen, the right common iliac artery 1600 issubstantially cylindrical, due to its strong, muscular construction(among other potential factors). That strong, muscular artery haspressed down on the left common iliac vein 1601, until it has almostcompletely lost patency, i.e., it is nearly completely pinched off. Itwill be understood that May-Thurner syndrome may indeed involve suchsevere pinching/crushing of the underlying left common iliac vein 1601against the vertebra 1602 of the lumbar spine. However, it will also beunderstood that May-Thurner syndrome may involve much lesspinching/crushing of the underlying left common iliac vein 1601 againstthe vertebra 1602. Indeed, embodiments disclosed herein are appropriatefor the treatment of various degrees of May-Thurner syndrome, includingfull crushing/pinching of the left common iliac vein 1602 by the rightcommon iliac artery 1600. Other embodiments disclosed herein areappropriate for the treatment of various degrees of May-Thurnersyndrome, including, but not limited to a crush/pinch of the underlyingleft common iliac vein 1601 of between about 10-95%, about 15-90%, about20-85%, about 25-80%, about 30-75%, about 35-70%, about 40-65%, about45-60%, and about 50-55%, or any other crush/pinch that could merittreatment using one or more of the devices disclosed herein.

Generally, disclosed herein are stents that include circumferentialrings of alternating interconnected struts connected by flexibleconnectors. The stent may have open or closed cells of variousconfiguration formed by an expandable material. The final expandedimplanted configuration can be achieved through mechanicalexpansion/actuation (e.g., balloon-expandable) or self-expansion (e.g.,Nitinol). An exemplary embodiment of the stents described herein areself-expanding implants comprising super elastic or shape memory alloymaterials, but the stent is not so limited and may be formed ofballoon-expandable material. According to an aspect of the presentdisclosure, an expandable stent has varying magnitudes of radial force,crush resistance and flexibility at different locations along the lengthof the stent, while at the same time, the different locations have thesame or similar diameter in an expanded configuration of the stent.

As illustrated in FIG. 6, an exemplary stent 10 includes a highradial/crush force segment 14, a highly flexible segment 18 and atransition segment 22 between the high radial/crush force segment 14 andthe highly flexible segment 18. The exemplary stent 10, as illustratedin FIG. 6, may include a reinforcement ring 26 at an end of the stent10, for example, adjacent the highly flexible segment 18 (configurationshown) or adjacent the high radial/crush force segment 14 (configurationnot shown). In an embodiment according to principles described herein,the stent 10 having a high radial/crush force segment 14 and a highlyflexible segment 18 may be cut from a single tube, such as nitinol, forexample, but could also be formed or cut from flat sheets that arewelded together at long edges to form a tube-like structure. While atransition segment is illustrated herein, it should be noted that ahybrid stent that does not include a transition segment is considered tobe within the scope of this disclosure.

Generally radial force refers to both or either Radial Resistive Force(RRF) and Chronic Outward Force (COF). As shown in FIG. 4, radialresistive force is an external force that acts around the circumferenceof a stent on the stent (toward the center of the stent). Chronicoutward force is the force the sent exerts outward from a direction ofthe center of the stent. Chronic outward force of a stent will cause thestent to exert force on the vessel in which it is inserted to resistcollapse and keep the vessel open. FIG. 5 illustrates crush resistance,as used herein. Crush resistance is a force of the stent when subject toa flat plate/focal crush load. While the radial force vector directionsin FIG. 6 illustrate chronic outward force, the radial force accordingto principles of the present disclosure may be radial resistive force,which is more related to crush resistance than a chronic outward force.Vectors illustrated in the figures are meant to indicate direction, notmagnitude. Although Radial Force and Crush Resistance can be relatedthey do not necessarily drive each other. So a stent may be designed tohave high crush resistance (flat plate/focal) but not high radial force.Such attributes can be tested independently in different testconfigurations.

The reinforcement ring may be an area of greater stiffness/crushresistance at an end portion of the stent. “Greater stiffness” heremeans having a stiffness/crush resistance greater than a portion of thestent adjacent the reinforcement ring. The reinforcement ring havinggreater stiffness may provide good inflow into the stent and through thevessel having the implant therein. While described herein as a“reinforcement ring,” the area of greater stiffness may be provided byan additional structure overlying the stent end (e.g., a “ring”) or mayinstead be an area where the strut structure is actually stronger, e.g.because the material forming the area of greater stiffness is inherentlystiffer, a tighter cell structure, thicker struts or the like. Forexample, the reinforcement ring may have a different stent geometry,e.g., different strut width or is simply a fully-connected ring.

An exemplary embodiment of the reinforcement ring is illustrated in FIG.7. As can be seen in FIG. 7, more of the ring struts making up thereinforcement ring are connected by flexible connectors/bridges to theadjacent ring than in the neighboring highly flexible segment.

Returning to the stent structure, as illustrated in FIG. 6, a length ofstent 10 having length L0 includes high radial force segment 14 having aradial force and/or crush resistance RF1 and a flexibility F1 along thelength L1 of the high radial/crush force segment 14. That is, aradial/crush resistive force RF1 of the high radial/crush force segment14 is relatively greater than the remainder of the stent 10, and may bein the range of 0.75 to 1.00 N/mm, for example. The flexibility F1 ofthe high radial/crush force segment 14 may also be relatively lower thanthe remainder of the stent 10. Flexibility is evaluated/measured throughangle of deflection. According to principles described herein, the highradial/crush force segment may be designed to withstand long termdurability (fatigue) testing with a flexion range of 0-60 degrees.

The relatively high radial/crush force segment 14 is intended to beplaced in a vessel in the region of the vessel prone to compression orcrushing, such as pinching/crushing of the underlying left common iliacvein 1601 against the vertebra 1602 caused by May-Thurner syndrome, asillustrated in FIG. 3. The high radial/crush force segment has adiameter D1.

The length of stent L0 also includes a highly flexible segment 18, whichhas relatively greater flexibility than the high radial/crush force 14segment along the length of the highly flexible segment 18. In addition,according principles of the present disclosure, the highly flexiblesegment 18 has a length L2, a diameter D2 and radial force, crushresistance RF2 and flexibility F2, where RF2<RF1 and F2>F1, such thatthe highly flexible segment is more flexible than the high radial/crushforce segment 14. According to principles described herein, the highlyflexible segment may be designed to withstand long term durability(fatigue) testing with a flexion range of 0-140 degrees. A radialresistive force RF2 of the highly flexible segment 18 may be in therange of 0.50 to 0.70 N/mm, for example.

The length of stent 10 may also include a transition segment 22 betweenthe high radial/crush force segment 14 and the highly flexible segment18, where the transition segment 22 has a length L3, a diameter D3 andradial force or radial resistive force (crush resistance) RF3 andflexibility F3, where RF1>RF3>RF2 and F1 and F2>F3>F1. The radial forceor radial resistive force (crush resistance) RF3 and flexibility F3 ofthe transition segment 22 may vary over the length L3 of the transitionsegment 22 or may be constant along the length L3 of the transitionsegment 22.

Each of the high radial/crush force segment 14, transition segment 22and highly flexible segment 18 has a different radial force, crushresistance and flexibility, which may be provided by different ringstructures in each segment of the stent 10. As can be observed in FIG.6, a high radial force segment 14 may have a cell structure that hasrelatively greater periodicity, may be formed of stiffer ring struts andflexible connectors, and/or may have a more closed cell structure orother structure to impart the desired radial force or crush resistancerelative to the radial force or crush resistance of the highly flexiblesegment. For example, the strut geometry, thicker/wider struts providemore radial strength, number of apexes around the circumference of thestent/ring geometry can all drive radial force up or down, and theconfiguration/connection to the adjacent rings through the bridgeconnectors and more ring connectors can increase radial force.Similarly, the highly flexible segment 18 may have a cell structure thathas relatively lesser periodicity, may be formed of relatively moreflexible ring struts and flexible connectors, and/or have a more opencell structure. The transition segment may have a cell structure thattransitions a geometry of the rings struts and flexible connectors ofthe high radial/crush force segment to a geometry of the highly flexiblesegment, or the transition segment may have a different cell structurethan the high radial/crush force segment and the highly flexiblesegment. In an embodiment according to principles described herein, thestent having a high radial/crush force segment, a transition segment anda highly flexible segment may be cut from a single tube, such asnitinol, for example, but may also be formed by any other suitablemeans.

In the illustrated embodiment of FIG. 6, each of the segments of thestent has substantially the same diameter, such that D1≈D2≈D3. Inanother embodiment, the stent can be tapered such that D1>D2>D3. Asdescribed herein, one stent can treat a range of vein vessel diameters.The present stent structure may allow a single stent to treat multiplevessel sizes as the force exerted on the vessel remains fairlyconsistent over a range of diameters (3-4 mm). This is different thanconventional stents in that most conventionally stents need to bespecifically sized to the vessel they are treating (i.e., 0.5 mm-1.0 mmof oversizing). Thus, most conventional stents are offered in 2 mmincrements (e.g., 10 mm, 12 mm, 14 mm, etc.). Adaptive diameteraccording to principles described herein simplifies sizing decisions forthe doctor and allows a single stent to treat a long segment of vein, asthe vein diameter generally reduces in diameter in the proximaldirection.

It is contemplated that the length L2 of the highly flexible segment 18will be greater than the length L1 of the high radial/crush forcesegment which will be greater than the length L3 of the transitionsegment.

An exemplary embodiment structure of a stent 110 according to principlesof the present disclosure is shown in FIG. 8. As illustrated in FIG. 8,the diameter DS along the stent 110 at any given ring 112 issubstantially the same (D1≈D2≈D3). In the embodiment illustrated in FIG.8, each of the high radial/crush force segment (May-Thurner Syndrome“MTS” Section) 114, the transition segment (Transition Section) 122 andthe highly flexible segment (Main Body Section) 118, has a similar cellpattern. In such case, the radial force or crush resistance RF of thesegments may be varied by varying the thickness of the struts and/orflexible connectors 132 or the angular relationship of the struts withother struts and/or with the flexible connectors and/or the angulationof the flexible connectors themselves.

It should be noted that terms such as perpendicular, thickness, same,similar, and other dimensional and geometric terms should not beregarded as strict or perfect in their application. Instead, geometricand other dimensional reference terms should be interpreted based ontheir correspondence to accepted manufacturing tolerances and functionalneeds of the stent 110 on which they are employed. For example, the term“perpendicular” should be appreciated as affording a reasonable amountof angular variation due to manufacturing imperfections or the actualintentional curves cut or formed in the stent design 110. Also, anythickness, width or other dimension should be assessed based ontolerances and functional needs of the design rather than idealizedmeasurements.

The thickness of the strut 128, on the other hand, is its depth in theradial direction which is generally perpendicular to the strut widthmeasurement, as shown in FIG. 8. The strut thickness 128 normallycorresponds to the wall thickness (outside diameter minus insidediameter) of the tube from which the stent 110 is laser cut afteretching, grinding and other processing. But, embodiments of the stentsdisclosed herein are not necessarily limited to being laser-cut from acylindrical tube with a predetermined wall thickness. They could also beformed or cut from flat sheets that are welded together at long edges toform a tube-like structure.

Each of the rings 112 is comprised of a plurality of ring struts 128interconnected to form alternating peaks or apexes 120 and troughs 124.As shown in FIG. 8, each of the ring struts 128 is generally straight.In one embodiment shown in FIGS. 8-9, a stent 110 includes a pluralityof rings 112 connected by a plurality of flexible connectors 132. Therings 112 are arranged in a spaced relationship along a long axis 116 ofthe stent 110. The connectors 132 extend between adjacent pairs of therings 112. Each of the rings 112 and connectors 132 are comprised of aplurality of interconnecting struts. The dimensions and orientation ofthese struts are designed to provide flexibility and radial/crushstiffness according to principles of the present disclosure.

The exemplary hybrid stent 110 illustrated in FIG. 8 may be made ofNitinol tubing that is superelastic per ASTM F2063. The stentspecification may further be as follows, post electropolishing: AFtemperature of parts to be 19+/−10 degrees Celsius. The hybrid stent maybe designed to treat a range of iliofemoral veins ranging in size from12 mm to 20 mm. These dimensions are exemplary and a stent according toprinciples of the present disclosure are not so limited.

FIGS. 9A, 9B and 9C illustrate details of the strut and connectorstructure of the high radial/crush force segment 114 (FIG. 9A) and thehighly flexible segment 118 (FIG. 9B) of the embodiment FIG. 8 at thelocations indicated in FIG. 8. FIG. 9C is showing detailed dimensions ofthe eyelet 119 geometry in which a radiopaque (RO) marker will beinserted to aid the doctor with deployment location of the stent underfluoroscopy.

FIG. 9A illustrates ring struts 128 a of the high radial/crush forcesegment 114. FIG. 9B illustrates ring struts 128 b of the highlyflexible segment 118.

As can be appreciated, foreshortening of the stent can be a particularproblem for placement of a stent. In practice, stents with greaterflexibility tend to foreshorten more. Accurate placement is ideal in allmedical interventions, but it is of great interest in areas where theend that is first deployed is important. Such areas include at vesselbifurcations and branch vessels, so that the implant does not enter orinterfere with the portion of the vessel that does not requiretreatment. Such a bifurcation is present at the inferior vena cava whereit branches into right and left iliac veins, as described in more detailbelow.

As described herein, a stent according to principles described hereinincludes a high radial/crush force segment and a highly flexiblesegment. The high radial/crush force segment, with its stifferstructure, will have minimal foreshortening, and as a result, can allowfor more accurate placement in the vessel into which it is implanted.FIG. 10 illustrates a rough placement of a stent according to principlesof the present disclosure. FIG. 10 illustrates the inferior vena cava1503 branching into the left common iliac vein 1504 and right commoniliac vein 1505. It will be understood that the rough diagramillustrated in FIG. 10 represents the view looking down on a patientlaying face-up (i.e., an anterior-poster view of the patient at thelocation of the bifurcation of the inferior vena cava 1503). For sake ofsimplicity, the abdominal aorta and its branching are not shown in FIG.10, but are shown in FIG. 2, above. In an aspect described herein,peak-trough configurations (e.g., if used with the highly flexiblesegment) may not appreciably foreshorten.

As illustrated in FIG. 10, a multi-segment stent 10 according toprinciples described is placed in the left common iliac vein 1504. Thehigh radial force segment 14 of the stent 10 may be allowed to extendinto the iliac vein 1503, although the end of the high radial forcesegment is intended to be placed to be at the junction of the leftcommon iliac vein 1504 and the iliac vein 1503. The highly flexiblesegment 18 extends away from the high radial force segment 14 and thetransition segment 22 between the highly flexible segment 18 and thehigh radial/crush force segment 14.

To facilitate placement of the stent 10 at the junction of the leftcommon iliac vein 1504 and the iliac vein 1503, the stent 10 may have aflared end adjacent the high radial force segment 14, as illustrated inFIG. 11. The distal flared section is controlled by radius ‘r’.Exemplary flare sizes include 2.5 mm×5.0 mm and 5.0 mm×5.0 mm, but stentflares according to principles of the present disclosure are not solimited. The flared distal end of the stent may be used for placement ofthe stent at a bifurcation of two vessels such as the common iliac vein1504 and the iliac vein 1503. The pre-loaded stent configuration on thedelivery system described herein allows the distal flared section of thestent to be partially deployed from the delivery system allowing theoperator to position the flared section of the stent at the bifurcationof two vessels. The delivery catheter is advanced central to the vesselbifurcation to be treated, in this case the left common iliac vein 1504.If radiopaque markers are provided on the implant, the operator can seatthe partially deployed flare section of the stent at the bifurcationjunction using the radiopaque markers. Once the central flared end ofthe partially deployed stent is in the appropriate deployment locationand seated at the bifurcation junction the remainder of the stent can bedeployed.

In an aspect of the present invention, a separate extension stent 50 maybe included along with the stent 10. An embodiment of the separateextension stent 50 is illustrated in FIG. 12. As illustrated in FIG. 12,the separate extension stent 50 is tubular and may be a highly flexiblesegment similar to the highly flexible segment 18 in the hybrid stent 10described above. In an aspect of the present disclosure, the separateextension stent 50 may comprise a plurality of rings 152, which comprisea plurality of ring struts 158 interconnected to form alternating peaksor apexes 160 and troughs 164. As shown in FIG. 12, each of the ringstruts 158 is generally straight. The ring struts 158 may be connectedto flexible connectors 162. The rings 152 are arranged in a spacedrelationship along a long axis 116 of the stent 110. The flexibleconnectors 162 extend between adjacent pairs of the rings. The separateextension stent 50 may also include reinforcement rings on either orboth ends of the tube. The dimensions and orientation of these strutsare designed to provide flexibility and radial/crush stiffness accordingto principles of the present disclosure. Each of the rings 152 andconnectors 162 comprises a plurality of interconnecting struts. Theseparate extension stent is made of an expandable material or aself-expandable material, such as Nitinol. The separate expansion stent50 may be cut from a single tube, such as nitinol, for example, butcould also be formed or cut from flat sheets that are welded together atlong edges to form a tube-like structure.

An exemplary extension stent is illustrated in FIG. 13. The extensionstent illustrated in FIG. 13 may be made of nitinol tubing that issuperelastic per ASTM F2063. The stent specification may further be asfollows, post electropolishing: AF temperature of parts to be 19+/−10degrees Celsius. The extension stent may be designed to treat a range ofiliofemoral veins ranging in size from 8 mm to 16 mm. These dimensions,as well as dimensions illustrated in the figures, are exemplary and astent according to principles of the present disclosure are not solimited.

The separate extension stent 50 is placed in the left iliac vein 1504adjacent the highly flexible segment 18 of the hybrid stent 10 and mayoverlap the end of hybrid stent 10, as illustrated in FIG. 14. Theregion of overlap in the illustration is indicted by reference number200. The placement of the hybrid stent 10 and the separate extensionstent 50 may be performed using the same delivery device at the sametime. A second delivery catheter with pre-crimped extension stent may beintroduced into the treatment vessel and approximate the proximal end ofthe previously deployed hybrid stent. The catheter with crimpedextension stent would be inserted into the proximal end of the hybridstent, positioned and the stent would be deployed utilizing theradiopaque markers on both stents to achieve appropriate overlap, e.g.,1 cm. In another aspect, the extension stent can be implanted as astand-alone stent.

It should be noted that an extension stent as described herein may beused in combination with other stents as a “main stent”, besides thehybrid stent 10. In use, the extension stent can be used to allow forvariation in placement.

In addition, the extension stent may include reinforcement rings wherethe reinforcement ring may be an area of greater stiffness/crushresistance at an end portion of the stent. “Greater stiffness” heremeans having a stiffness greater than a portion of the sent adjacent thereinforcement ring. The reinforcement ring having greater stiffness mayprovide good inflow into the stent and through the vessel having theimplant therein. The reinforcement rings may make the extension stenteasier to place with respect to the main stent, for example, bymitigating crushing of the ends as they are made to overlap. Inaddition, to facilitate placement, the ends of the extension stentand/or the stent to which it is to be placed adjacent can be coated witha polymer, such as urethane or PTFE. Also, the extension stent mayinclude anchors, eyelets, radiopaque markers or other features to assistin placement of the extension stent. The extension stent may also bedelivered with the main stent, or may be separately delivered to thevessel.

The extension stent may be delivered via an appropriate access site,(e.g. jugular, popliteal, etc.). The extension stent can be made to be“bidirectional”, such that it could be preloaded onto a deliverycatheter without specific regard to the direction of the delivery (e.g.,jugular, popliteal, etc.). E.g. the delivery can be made from above thetreatment region or from below the treatment region. Suchbidirectionality can be facilitated by the extensions stent geometrybeing symmetrical such that ends of the extension stent have the samegeometry. The stent may be delivered by a coaxial delivery catheter. Inanother aspect of the present disclosure, a novel delivery device mayinclude a cartridge that may be loaded onto a catheter and the hybridsent also loaded on the catheter. The cartridge can be flipped by theoperator for retrograde or anterograde. The stent may be preloaded ontothe delivery catheter for the direction of the delivery (e.g., jugular,popliteal, etc.)

As can be appreciated, the actual stent ring geometry may vary from thatdisclosed herein, as long as the stent 10 includes a first section witha relatively higher radial force or crush resistance than a secondsection of the stent that has a relatively higher flexibility than thefirst section. It is also contemplated that the separate extension stent50 have a flexibility similar to the highly flexible segment of thehybrid stent 10. Exemplary stent geometries for segments of the hybridstent 10 and the extension stent 50 are taught in U.S. patentapplication Ser. Nos. 15/471,980 and 15/684,626, which are herebyincorporated by reference for all purposes as if fully set forth herein.

FIGS. 15A and 15B illustrate a “cut” (planar/flattened) view of anexemplary embodiment of a high radial/crush force segment of a stent ina compressed state according to principles of the present disclosure.FIG. 15A illustrates a stent geometry for the high radial/crush forcesegment 214 of a stent according to principles described herein. FIGS.15A and 15B illustrate the exemplary high radial/crush force segment ina compressed state. FIG. 15B illustrates a magnified view of apices ofthe high radial/crush force segment of the embodiment illustrated inFIG. 15A according to principles of the present disclosure. Theexemplary high radial/crush force segment 214 includes a plurality ofrings 212 connected by a plurality of connectors 232. The rings 212 arearranged in a spaced relationship along a long axis of the stent highradial/crush force segment 214. The connectors 232 extend betweenadjacent pairs of rings 212. Each of the rings 212 is comprised of aplurality of interconnecting struts 228. The dimensions and orientationof these struts are designed to provide a relatively high radial/crushforce such that the stent segment has a higher crush resistance than theadjacent transition segment or the highly flexible segment, (see FIGS. 6and 8).

Each of the rings 212 is comprised of a plurality of ring struts 228interconnected to form alternating peaks or apexes 240 and troughs 242.As shown in FIGS. 15A and 15B, each of the ring struts 228 is generallystraight and has a main strut width 224 and a strut length 230. The mainstrut width 224 is the width of the strut in the circumferentialdirection but adjusted to be at about a right angle to the edge of thestrut. In other words, the main strut width 224 is an edge to edgemeasurement corresponding to the outermost circumferential surface ofthe struts of the rings 212

Each of the connectors 232 itself is comprised a connector strut 234. Inthe present embodiment, the connector is a single connector strut 234,but the connector design is not necessarily limited to a single strut.As illustrated in FIG. 15A, an end 236 of each connector strut 234connects to a respective ring strut 228. Each connector strut 234 in aplurality extends from its end that is connected to the respective ringstrut 228 in a respective ring 212 toward an adjacent ring 212. Theconnector strut 234 extends in a direction neither parallel norperpendicular to the longitudinal axis of the stent high radial/crushforce segment 214. As illustrated in FIG. 15A, in this aspect of thehigh radial force segment in the illustrated embodiment, the connectorconnects 232 to a ring strut 228 in an adjacent ring that is offset in alatitudinal direction from the ring strut from which it extends. Thatis, as illustrated, the connector 234 connect from a ring strut 228 to aring strut two places over from the one immediately adjacent—in theillustrated embodiment, there are two unconnected apices between twoconnected apices. In other words, in some embodiments, each ring strut228 is not necessarily connected to another ring strut in an adjacentring by a connector. It is possible, in another aspect, for each apex240 to connect to an apex 240 in an adjacent ring 212. In someinstances, those apices 240 may be connected by a connector 232 whoseconnection thereto is offset from the actual peak of the apex 240, asillustrated in detail in FIG. 15B. In some embodiments, the connectors232 do not connect directly to or at the apexes 240 of the rings 212.Instead, they are offset somewhat along the length of the ring struts228 to which they are connected. Also, in some embodiments, asillustrated in FIG. 15A, connectors 232 on either side of a ring 212 are“wound” in opposite directions (e.g., clockwise and counter clockwisedirections) in a compressed configuration.

The connector struts 234—similar to the ring struts 228 of the exemplaryembodiment—have a relatively constant width except where they connect tothe rings 212. As with the ring struts 228 described above, the width ofthe connector struts 234 may enlarge somewhat as they merge intoconnections with the rings 212. As shown in FIG. 15B, for example, eachof the connectors 232 also includes a main connector width 256 (betweenarrows) and an apex connector width 258 (between arrows). The mainconnector width 256 is the width of the connector strut 228, usually theminimum width or width expressing the area of highest flexibility, ofthe strut between the rings 212 and the connector apex 240. The apexconnector width 258 is the width of the connector apex 240 somewherealong its bend, such as in the middle of the bend. In any case, the apexconnector width 258 can be a structural expression of an area of highflexibility on the connector apex 240.

FIG. 16 illustrates an exemplary embodiment of a high radial/crush forcesegment of a stent in an expanded state according to principles of thepresent disclosure. As illustrated in FIG. 16, upon expansion of thecompressed high radial force segment 228 illustrated in FIG. 15A, therings 212 rotate such that the apexes of each ring 212 iscircumferentially aligned between the apexes of the adjacent ring 212,through the design of the length of the connectors 232. In someembodiments, such as larger stents (e.g., outer diameters in theapproximate range of 16-20 mm) the flexible connectors between and MTSsection and a transition section may have “straight” connectors (in anexpanded state), e.g. extending substantially in the axial direction ofthe stent. In other embodiments, such as smaller stents (e.g. outerdiameters in the approximate range of 12-14 mm) may have angled stentsin an expanded state, e.g. extending in a direction not substantially inthe axial direction of the stent. While these embodiments are mentionedhere, it is possible that any size stent may have “straight” connectorsand/or “angled” connectors in the expanded state.

FIG. 17A illustrates a planar/flattened view of an exemplary embodimentof a flexible segment and an exemplary embodiment of a reinforcementsegment of a stent in a compressed state according to principles of thepresent disclosure. FIG. 17B illustrates a magnified view of apices ofthe flexible segment of the embodiment illustrated in FIG. 17A accordingto principles of the present disclosure. FIG. 17C illustrates amagnified view of apices of the reinforcement rings of the embodimentillustrated in FIG. 17A according to principles of the presentdisclosure.

As illustrated in FIG. 17A, the exemplary flexible segment 318 includesa plurality of rings 312 connected by a plurality of connectors 332. Therings 312 are arranged in a spaced relationship along a long axis of thestent flexible segment 318. The connectors 332 extend between adjacentpairs of rings 312. Each of the rings 312 is comprised of a plurality ofinterconnecting struts 328. The dimensions and orientation of thesestruts are designed to provide a relatively higher flexibility such thatthe stent segment has a greater flexibility than the adjacent transitionsegment or the high radial/crush force segment, (see FIGS. 6 and 8).

Each of the rings 312 is comprised of a plurality of ring struts 328interconnected to form alternating peaks or apexes 340 and troughs 342.As shown in FIGS. 17A and 17B, each of the ring struts 328 is generallystraight and has a main strut width 324 and a strut length 330. The mainstrut width 324 is the width of the strut in the circumferentialdirection but adjusted to be at about a right angle to the edge of thestrut. In other words, the main strut width 324 is an edge to edgemeasurement corresponding to the outermost circumferential surface ofthe struts of the rings 312

Each of the connectors 332 itself is comprised a connector strut 334. Inthe present embodiment, the connector 332 is a single connector strut334, but the connector design is not necessarily limited to a singlestrut. As illustrated in FIG. 17A, an end 336 of each connector strut334 extends from a trough 342 to an apex in an adjacent ring 312. In theexemplary embodiment, the connector strut 334 extends in a directionsubstantially parallel to the longitudinal axis of the stent flexiblesegment 318. As illustrated in FIG. 17A, in this aspect of the flexiblesegment in the illustrated embodiment, every fourth trough 342 isconnected by a connector 332 to an apex 340 in an adjacent ring 312.That is, as illustrated, three adjacent troughs are not connected to theadjacent ring by a connector 332. In other words, in some embodiments,each trough is not necessarily connected to an apex 340 in an adjacentring by a connector. It is possible, in another aspect, for each trough342 to connect to an apex 340 in an adjacent ring 312. In someembodiments, although not shown, the connectors 332 may not connectdirectly to or at troughs 342 or the apexes 340 of the rings 312.Instead, they are offset somewhat along the length of the ring struts328 to which they are connected. Also, in some embodiments, asillustrated in FIG. 15A, connectors 332 on either side of a ring 212 are“wound” in opposite directions (e.g., clockwise and counter clockwisedirections).

The connector struts 334—similar to the ring struts 328 of the exemplaryembodiment—have a relatively constant width except where they connect tothe rings 312. The width of the connector struts 334 may enlargesomewhat as they merge into connections with the rings 312. FIG. 18illustrates an exemplary embodiment of a flexible segment 318 of a stentin an expanded state according to principles of the present disclosure.

The exemplary reinforcement ring segment 426 includes a plurality ofrings 412 connected by a plurality of connectors 432. The rings 412 arearranged in a spaced relationship along a long axis of the reinforcementrings 426. The connectors 432 extend between adjacent pairs of rings412. Each of the rings 412 is comprised of a plurality ofinterconnecting struts 428. The dimensions and orientation of thesestruts are designed to provide a relatively greater radial force suchthat the stent segment has a higher crush resistance than the adjacenttransition segment or the highly flexible segment, (see FIGS. 6 and 8).The present figures illustrate connectors 432 as horizontalwith/parallel to the stent axial direction, but they could also beangled, and adjacent rings can be orientated such that apex-apex betweenrings are not aligned, as illustrated in FIG. 21. This connectionpattern may be used at the end rings of the extension stent 50.

Each of the rings 412 is comprised of a plurality of ring struts 428interconnected to form alternating peaks or apexes 440 and troughs 442.As shown in FIGS. 17A and 17C, each of the ring struts 428 is generallystraight and has a main strut width 424 and a strut length 430. The mainstrut width 424 is the width of the strut in the circumferentialdirection but adjusted to be at about a right angle to the edge of thestrut. In other words, the main strut width 424 is an edge to edgemeasurement corresponding to the outermost circumferential surface ofthe struts of the rings 312

Each of the connectors 432 itself may be comprised of a connector strut434. In the present embodiment, the connector 432 is a single connectorstrut 434, but the connector design is not necessarily limited to asingle strut. As illustrated in FIG. 17A, an end 436 of each connectorstrut 432 extends from an apex 440 to an apex 440 in an adjacent ring412. In the exemplary embodiment, the connector 432 extends in adirection substantially parallel to the longitudinal axis of the stentreinforcement ring 412. As illustrated in FIG. 17A, in this aspect ofthe reinforcement segment 426 in the illustrated embodiment, every apex440 is connected by a connector 432 to an apex 440 in an adjacent ring412. In other words, in some embodiments, each apex is connected to anapex 440 in an adjacent ring by a connector 432. It is possible, inanother aspect, for not all apices 440 to connect to an apex 440 in anadjacent ring 412. In some embodiments, although not shown, theconnectors 432 may not connect directly to or at apexes 440 of the rings412. Instead, they are offset somewhat along the length of the ringstruts 428 to which they are connected.

The connector 432—similar to the ring struts 428 of the exemplaryembodiment—have a relatively constant width except where they connect tothe rings 412. The width of the connector struts 432 may enlargesomewhat as they merge into connections with the rings 412 or ringapices 440. FIG. 18 illustrates an exemplary embodiment of thereinforcement ring segment 426 of a stent in an expanded state accordingto principles of the present disclosure.

FIG. 17A also illustrates a transition portion where the flexiblesegment 318 connects to the reinforcement segment 426. As illustrated bythe connection of the third ring from the right 512 in FIG. 17A, aconnector 332 extends from a trough 340 from a ring 312 of the flexiblesegment 318 and connects to an apex 540 a in the adjacent ring 512(second ring from the right in FIG. 17A). On the opposite side of ring512, each apex 540 b of the ring 512 connects to apices 440 in adjacentring 412. Accordingly, transition between the flexible segment 318 tothe reinforcement segment 426 is accomplished.

A hybrid stent 510 having separate segments of varying radial/crushforce and flexibility according to principles described herein maybenefit from a smooth transition between segments. In an aspect of thepresent hybrid stent, the high radial/crush force segment may includerings along the length of the stent that are designed to rotate withrespect to one another, and the transition and flexible region, wherethe stent opens more uniformly, may have no rotation. Thus, an aspectmay allow for smooth transition between two adjacent regions/segments ofthe stent to address crimp and deployment issues that may result fromthe twist of the last ring of the high radial/crush force segmentcreating a twist in the adjacent transition/flexible segment region.FIG. 19 illustrates an embodiment of transitions between segments thatenable a segment that has rotating/twisting rings when beingcollapsed/crimped or during expansion when being deployed to beconnected to a segment that does not twist but has additional means ofbeing flexible. FIG. 19 illustrates straight connection transition froma rotating segment (left) of, e.g., a high radial force segment 518, toa non-rotating segment (right), e.g. a transition segment 522. Thestraight connection in the exemplary embodiment includes a plurality ofstraight connectors 532. The straight connection at that junctionenables a uniform crimp and reduces or eliminates the twisting andcrimping issues.

FIG. 20 illustrates an exemplary connection between a high radial forcesegment (MTS segment) (left) 618 and a transition section (right) 622according to principles described herein that may be applicable insmaller hybrid stents, such 12-14 mm stents. The illustrated connectionand each respective illustrated segment is but one stent geometry.

It is noted that the struts of the rings and flexible connectors withstructure, including areas of expanded or reduced width or thickness, toaccount for venous applications, may be used. As another example, it isnoted that venous applications benefit from configurations that improveflexibility (due to the greater elasticity of venous applications) whilemaintaining enough stiffness to resist pressure on the venous structurein selected areas (such as for the May-Thurner syndrome).

Notably the stents herein are not necessarily limited to venousapplications unless specifically required by the claims. The disclosedstents could be employed in arterial and biliary applications, forexample. But, are particularly suited for the demands of relatively softstructures defining lumens that are subject to much greater bending,twisting, stretching and other contortions and loads than are generalarterial lumens.

To deploy the implant, the implant may be radially compressed/crimped toa smaller diameter for loading onto/into a delivery catheter. Theimplant may be crimped over a balloon on the inner core of the deliverysystem which may be later inflated to expand the crimped implant to thedesired diameter.

Implants such as those described above may advantageously provide anadaptive diameter and/or flexibility to conform the dynamic movement ofperipheral veins in leg/pelvis thereby facilitating treatment of bothiliac vein compression syndrome and iliofemoral venous outflowobstructions.

It may be desirable to have a stent that will conform to the existingpath of a vein instead of a straightening out of the vessel by thestent. It may also be desirable to have a high radial/crush stiffness ofthe stent to resist collapse of the stent under crushing load and tomaximize the resultant diameter of the treated vessel at the location ofthe stent deployment. With most stent constructions there is a directrelationship between radial stiffness and axial stiffness.

Common commercially available balloon expandable stents experience adramatic change in length as a balloon is used to expand the stentwithin the vessel. Common commercially available self-expanding stentsexperience a change in length less dramatic, but still substantial,which increases with increasing stent length. Change in length betweenthe configuration within the delivery system and when deployed in thevessel causes difficulty in placing/landing the stent precisely at thetarget location. When the stent is delivered in its crimpedconfiguration, then deployed or expanded, the shortening in lengthcauses the stent target deployment location to have to offset from thetarget dwell location. The magnitude of this effect is not controllableor easily anticipated as it is dependent on the luminal cross-sectionalong the length of the target dwell location (which is frequently andunexpectedly influenced by residual stenosis, irregular shape due toexternal objects, and/or forces, etc.). For target lesions leading up tothe junction of the left and right iliac into the IVC, this causesdifficulty in placing the stent to dwell completely within the iliacalong its total length up to the junction to the inferior vena cavawithout crossing into the inferior vena cava. Placement of a highradial/crush force segment at the junction not only assists inaddressing crush by May-Thurner Syndrome, but also may assist inreducing foreshortening from the target location.

Embodiments disclosed herein can be used for both balloon expandable andself-expanding stent designs. The stent designs can be used for allstent interventions, including coronary, peripheral, carotid, neuro,biliary and, especially, venous applications. Additionally, this couldbe beneficial for stent grafts, percutaneous valves, etc.

Currently available implants are typically loaded and retained onto adelivery system in a crimped configuration and then navigated anddeployed in the desired anatomical location where they expand to theimplanted configuration. The final implanted configuration can beachieved through mechanical expansion/actuation (e.g.,balloon-expandable) or self-expansion (e.g., Nitinol). Self-expandingimplants are manufactured from super elastic or shape memory alloymaterials. Accurate and precise deployment of a self-expanding implantcan be challenging due to a number of inherent design attributesassociated with self-expanding implants. The implant may jump/advancefrom the distal end of the delivery system during deployment due to thestored elastic energy of the material. Additionally, the implant mayforeshorten during deployment due to the change in the implant diameterfrom the crimped configuration to the expanded configuration. Finally,physiological and anatomical configurations, such a placement at or nearbifurcations of body lumens, can affect accurate placement of implants.Once the implant is placed within the body lumen there is potential foruneven expansion or lack of circumferential implant apposition to thebody lumen which can result in movement, migration or in certain severecases implant embolization.

In some embodiments, a self-expanding implant designed with sufficientradial force or crush resistance to resist constant compression of thebody lumen while providing optimal fatigue resistance, accurateplacement, and in-vivo anchoring to prevent movement/migration isprovided. Additionally, various methods for deployment and implantationfor treating iliac vein compression syndrome and venous insufficiencydisease are provided.

In some embodiments, the implant comprises a purposely designed venousimplant intended to focally treat iliac vein compression (May-ThurnerSyndrome). The implant may be relatively short in length (−60 mm) andmay be manufactured from self-expending Nitinol with integrated anchorfeatures to aid in accurate placement and to mitigate migrationfollowing implantation. The implant and delivery system are designed forprecise deployment and placement at the bifurcation of the inferior venacava into the right and left common iliac veins.

As another feature, the stents disclosed herein can include anchormembers, radiopaque markers, or eyelets, for example, set forth inpending U.S. patent application Ser. Nos. 15/471,980 and 15/684,626,which are hereby incorporated by reference for all purposes as if fullyset forth herein.

Although this invention has been disclosed in the context of certainembodiments and examples, it will be understood by those skilled in theart that the present invention extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses of theinvention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the invention have been shownand described in detail, other modifications, which are within the scopeof this invention, will be readily apparent to those of skill in the artbased upon this disclosure. It is also contemplated that variouscombinations or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theinvention. Accordingly, it should be understood that various featuresand aspects of the disclosed embodiments can be combined with orsubstituted for one another in order to form varying modes of thedisclosed invention. Thus, it is intended that the scope of the presentinvention herein disclosed should not be limited by the particulardisclosed embodiments described above but should be determined only by afair reading of the claims that follow.

Similarly, this method of disclosure, is not to be interpreted asreflecting an intention that any claim require more features than areexpressly recited in that claim. Rather, as the following claimsreflect, inventive aspects lie in a combination of fewer than allfeatures of any single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be apparent to persons skilledin the relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the presentinvention. Thus, the breadth and scope of the present invention shouldnot be limited by any of the above-described exemplary embodiments butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A stent, comprising: a first stent segmentcomprising a plurality of first rings contiguously connected to oneanother to form a series of said first rings, the first ringscomprising: a plurality of first ring struts connected such that each ofthe plurality of first rings comprises a sinusoidal pattern having aplurality of apices and troughs, each first ring connected to anadjacent first ring by at least one connector, the connector extendingfrom a ring strut of the first ring from a position near an apex of saidfirst ring to a ring strut of the adjacent first rings near an apex ofthe adjacent ring, a second stent segment comprising a plurality ofsecond rings contiguously connected to one another to form a series ofsaid second rings wherein: the second stent segment is coupled to thefirst stent segment via a smooth transition region; each of theplurality of first rings having a first stiffness and a first crushresistance and each of the plurality of second rings having a secondstiffness and a second crush, wherein the first stiffness is differentfrom the second stiffness and the first crush resistance is differentfrom the second crush resistance.
 2. The stent of claim 1, furthercomprising at least one reinforcement ring coupled to one of the firstrings or one of the second rings, such that the at least onereinforcement ring is the end ring of said stent, the reinforcement ringhaving a third stiffness and a third crush resistance, where the thirdstiffness is different from the first stiffness and the second stiffnessand the third crush resistance is different from the first crushresistance and the second crush resistance.
 3. The stent of claim 1,wherein the first stent segment and the second stent segment havesubstantially the same diameter in an expanded state.
 4. The stent ofclaim 2, wherein the first stent segment, the second stent segment andthe reinforcement ring have substantially the same diameter in anexpanded state.
 5. The stent of claim 1, the second rings comprising: aplurality of second ring struts connected such that each of theplurality of second rings comprises a sinusoidal pattern having aplurality of apices and troughs, each second ring connected to anadjacent second ring by at least one connector, the connector extendingfrom a trough of the second ring to an apex of the adjacent second ring.6. The stent of claim 1, wherein each first ring is connected to theadjacent ring by a number of connectors fewer than the number of apicesof each first ring.
 7. The stent of claim 1, wherein the at least oneconnector extends in a direction non-parallel to a longitudinal axis ofthe first stent segment.
 8. The stent of claim 7, wherein the at leastone connector extends past at least one apex of the adjacent ring to aconnection point on the ring strut of the adjacent first ring in acompressed configuration.
 9. The stent of claim 7, wherein connectors oneither side of a first ring are wound in opposite directions in acompressed configuration.
 10. The stent of claim 2, wherein at least onereinforcement ring comprising a plurality of reinforcement ring strutsconnected such that the at least one reinforcement ring comprises asinusoidal pattering having a plurality of apices and troughs, andfurther comprising an additional reinforcement ring connected to the atleast one reinforcement ring by a reinforcement connector, wherein thereinforcement connector extends from an apex of the at least onereinforcement ring to an apex of the additional reinforcement ring. 11.The stent of claim 10, wherein each apex of the at least onereinforcement ring is connected to the additional reinforcement ring bya reinforcement connector.
 12. The stent of claim 1, wherein the secondstent segment is coupled to the first stent segment by a substantiallystraight connector connecting one of the plurality of second rings to anadjacent one of the plurality of first rings.
 13. The stent of claim 12,the second rings comprising: a plurality of second ring struts connectedsuch that each of the plurality of second rings comprises a sinusoidalpattern having a plurality of apices and troughs and wherein an apex ofthe adjacent one of the plurality of first rings is connected by thesubstantially straight connector to an apex of the one of the pluralityof second rings.
 14. The stent of claim 13, wherein a plurality ofapices of the adjacent one of the plurality of first rings are connectedto a plurality of apices of the one of the plurality of second rings,each apex of the adjacent one of the plurality of first rings connectedto a respective one of the plurality of apexes of the one of theplurality of second rings by the substantially straight connector. 15.The stent of claim 14, wherein the plurality of apices of the adjacentone of the plurality of first rings is fewer than all of the apices ofthe adjacent one of the plurality of first rings.
 16. The stent of claim14, wherein the plurality of apices of the one of the plurality ofsecond rings is fewer than all of the apices of the one of the pluralityof second rings.
 17. The stent of claim 13, wherein each connected apexof the adjacent one of the plurality of first rings is spaced fromanother connected apex of the adjacent one of the plurality of firstrings by an apex of the adjacent one of the plurality of first ringsthat is not connected to the one of the plurality of second rings. 18.The stent of claim 13, wherein each connected apex of the one of theplurality of second rings is spaced from another connected apex of theone of the plurality of second rings by an apex of the one of theplurality of second rings that is not connected to the adjacent one ofthe plurality of second rings.
 19. The stent of claim 1, whereinattachment of the at least one connector to the ring strut is offsetfrom the actual peak of the apex of the respective ring strut.
 20. Thestent of claim 13, wherein attachment of the substantially straightconnector to the one of the plurality of second rings is offset from anactual peak of the apex of the one of the plurality of second rings. 21.The stent of claim 1, wherein the first stent segment and the secondstent segment are end segments of said stent.
 22. The stent of claim 1,wherein the first stiffness is substantially constant along the lengthof the first stent segment and the second stiffness is substantiallyconstant along the length of the second stent segment.
 23. The stent ofclaim 1, wherein the first crush resistance is substantially constantalong the length of the first stent segment and the second crushresistance is substantially constant along the length of the secondstent segment.
 24. The stent of claim 1, further comprising a thirdstent segment between the first stent segment and the second stentsegment, the third stent segment comprising a plurality of third ringsconnected to one another to form a series of said third rings, the thirdstent segment having a third stiffness that varies along a length of thethird stent segment from the first stent segment to the second stentsegment.
 25. The stent of claim 1, further comprising a third stentsegment between the first stent segment and the second stent segment,the third stent segment comprising a plurality of third rings connectedto one another to form a series of said third rings, the third stentsegment having a third crush resistance that varies along the length ofthe third stent segment from the first stent segment to the second stentsegment.
 26. The stent of claim 1, wherein the first stent segmentcomprises at least three of the first rings and the second stent segmentcomprises at least three of the of the second rings.
 27. The stent ofclaim 24, wherein the second segment connected to the first segment viaa smooth transition comprises a plurality of flexible connectorsextending from adjacent at least one of the apices of the first stentsegment to adjacent at least one of the apices of the third stentsegment in a region adjacent the first stent segment and a plurality offlexible connectors extending from adjacent at least one of the apicesof the second stent segment to adjacent at least one of the apices ofthe third stent segment in a region of the third stent adjacent thesecond stent segment.
 28. The stent of claim 27, wherein adjacent atleast one of the apices includes offset from an actual peak of the apex.29. The stent of claim 1, wherein the smooth transition region comprisesa plurality of flexible connectors extending from adjacent at least oneof the apices of the first stent segment to adjacent at least one of theapices of the second stent segment.
 30. The stent of claim 29, whereinadjacent at least one of the apices includes offset from an actual peakof the apex.
 31. The stent of claim 1, wherein diameter of the firststent segment is substantially the same as the second stent segment inan expanded state.
 32. The stent of claim 24, wherein the diameter ofthe first segment, the second stent segment and the third stent segmentare substantially the same in an expanded state.
 33. The stent of claim25, wherein the diameter of the first segment, the second stent segmentand the third stent segment are substantially the same in an expandedstate.